The present invention relates in general to integrated circuits, and in particular to an input power measurement circuit for an adaptive battery charger.
With the proliferation of battery operated portable electronic devices. the demand for smaller and more efficient battery chargers has increased. To extend the life of the battery it is desirable to charge the battery even when the electronic device (e.g., laptop computer) is active and drawing power. One type of battery charger maximizes its efficiency by directing charge from the power source to the battery when the electronic device is powered up and operating, and depending on the level of power demanded by the electronic device. To implement this type of adaptive battery charging requires an accurate measurement of the input power available to the portable device. Existing battery chargers, such as one described in U.S. Pat. No. 5,698,964, assume a power source with a constant DC voltage, and measure the input power by a simple sensing of the input current. This technique, however, fails to address applications wherein the battery charger may be used in systems with varying power supply voltage levels.
Further, existing battery charger systems use fixed threshold levels to control the battery charging current and charging voltage. New types of batteries such as lithium ion batteries, however, have a variable charging cycle. That is, ideally a lithium battery is initially charged at a very fast rate up to e.g., 85-90%. Once it reaches that level, the charging must slow down to avoid over charging and over heating of the battery. Existing battery chargers with fixed charging threshold levels cannot support this type of variable charging.
There is a need for a more efficient and flexible battery char gin g circuitry that can operate with varying power supply voltage levels.